Numerous designs have been proposed to detect the presence of a localized magnetic field at a particular location and to discriminate it from the earth's relatively stable magnetic field. The earth's magnetic field may be locally distorted by the presence of a localized field. Many types of magnetometers are known in the art for magnetic field detection. Optical fibers have been employed in recent developments for sensing and measuring magnetic fields.
It is known to pass light through a pair of optical fibers, one defining a magnetic field sensing arm and the other a reference arm in the form of an interferometer, and compare relative phase shifts for providing an indication of a magnetic field. Such arrangements are disclosed in U.S. Pat. Nos. 4,376,248 and 4,433,291. In these patents, a magnetostrictive sleeve is fixedly carried on or about the g fiber defining the sensing arm. The magnetostrictive sleeve in the presence of a magnetic field undergoes dimensional changes to stress the fiber to cause a change in its index of refraction and optical path length which, in turn, causes a detectable phase change in light passing therethrough compared with light from a common source passing through the reference arm. Voltage of electricity flowing through a wire may be measured by optically measuring the strength of the magnetic field about the wire. In one embodiment, a plane of polarized light is passed through an optical fiber wound in the form of a coil. The plane is caused to rotate in one direction when the coil is placed in the presence of a magnetic field. This rotation is known as the Faraday effect. U.S. Pat. Nos. 3,324,394; 3,693,082 and 3,810,013 teach arrangement for measuring voltage in a line.
Another arrangement disclosed in U.S. patent application Ser. No. 179,134, filed July 28, 1980, by Sidney Reed for an optical fiber magnetometer, and likewise assigned to the U. S. Government, is for detecting the presence of a localized magnetic field. It employs a continuous optical fiber wound in the form of a loop about an elongate spindle which is located inside a bar of selected metal adapted for gathering or concentrating magnetic flux. The present application is an improvement over U.S. patent application Ser. No. 179,134 because it teaches an optical fiber wound in the form of a spheroid which provides for omnidirectional additive detection of all flux lines of both the earth and a localized source or sources.
The invention provides an improved arrangement for detecting a total magnetic field.